1. Field
The present disclosure relates to light emitting diodes with a thin phosphor layer.
2. Background
Solid state devices, such as light emitting diodes (LED)s, are attractive candidates for replacing conventional light sources such as incandescent and fluorescent lamps. LEDs have substantially higher light conversion efficiencies than incandescent lamps and longer lifetimes than both types of conventional light sources. In addition, some types of LEDs now have higher conversion efficiencies than fluorescent light sources and still higher conversion efficiencies have been demonstrated in the laboratory. Finally, LEDs require lower voltages than fluorescent lamps, and therefore, provide various power saving benefits.
LEDs produce light in a relatively narrow spectrum. To replace conventional lighting systems, LED-based sources that produce broad-spectrum (e.g., white) light are needed. One way to produce white light is to encapsulate blue or ultra-violet (UV) LEDs in a phosphor material. The phosphor material converts monochromatic light emitted from the blue or UV LEDs to white light.
The phosphor material is generally formed by introducing a suspension of phosphor particles into a carrier (e.g., silicone), encapsulating the LEDs in the carrier, and curing the carrier to provide a solid layer of material in which the phosphor particles will remain suspended. Unfortunately, silicone is a poor thermal conductor, and when illuminated, phosphors generate heat. Thus, when a phosphor-coated LED with a cured silicone carrier is used in a high-power application, the cured silicone may crack and/or have a reduced lifetime.
This property limits their use in high power LED applications which use temperature sensitive phosphor. Further, cracks in the phosphor and silicone composition reduce the efficiency of the device. Accordingly, there is a need in the art for simplified and improved processes for applying a phosphor material to LEDs and other solid state lighting devices.